Take the Heathrow Express train to Paddington Station. The travel time is about 15 minutes, and the train runs every 15 minutes.
From Paddington Station on the Underground (Tube), take a Circle Line train (yellow on the Tube map) to King's Cross Station, then take a Piccadilly line train (blue) to Holborn Station.
From Holborn Station on the Underground (Tube), exit the main front entrance and cross over at the traffic light so you are facing Sainsburys. Turn left, and walk down Kingsway until you reach Kemble Street on your righthand side, then take the first left into Kean Street. Kean House is located at 6 Kean Street.